Molecular Design of Fullerene Acceptors for High-Performance Bulk-Heterojunction Solar Cells
Organic bulk-heterojunction solar cells have attracted considerable research interest from both academia and industry because they have the advantages of light weight, low material cost, good mechanical flexibility, and simplicity of manufacture. Especially, recent advances in low-bandgap conjugated polymers and novel fullerene derivatives have further increased the PCE to 6-9%. The active layer in this type of solar cell is usually a binary blend of two compounds, with the one with a higher-lying LUMO acting as electron donor (D) and the other one as electron acceptor (A).
Because the excitons generated in organic materials typically have large binding energy and can only be efficiently dissociated into free carriers at the interface of D/A with the aid of the energetic driving force originating from the differences in the electronic levels of the materials. Since Heeger et al. discovered that C60 is an effective fluorescence quencher of conjugated polymer, fullerenes and their derivatives have been extensively used as acceptor materials in fabricating polymer solar cells. In this seminar, the design strategy of fullerene acceptors and the effect of their molecular structure on the photovoltaic performance will be systematically discussed.